ESTRO 2021 Abstract Book

S491

ESTRO 2021

Conclusion SBRT 3 x 8 Gy to a limited number of metastatic lesions, added concurrently to ICB does not appear to improve PFS.

OC-0626 Toxicity of SRT combined with targeted agents: prospective analysis of the TOaSTT database S. Kroeze 1 , J. Schaule 1 , M. Spaas 2 , K.H. Kahl 3 , J.J. Verhoeff 4 , F.L. Schneiders 5 , O. Blanck 6 , F. Lohaus 7 , S. Rogers 8 , D. Kaul 9 , S. Benavente 10 , S.E. Combs 11 , G. Skazikis 12 , K. Baumann 13 , I. Popp 14 , F. Koppe 15 , H. Geinitz 16 , K.E. de Jaeger 17 , S. Siva 18 , S. Stera 19 , A. Wittig-Sauerwein 20 , V. Lewitzki 21 , F. Eckert 22 , M.M. Schymalla 23 , M. Guckenberger 24 1 University Hospital Zürich, Radiation Oncology, Zürich, Switzerland; 2 Ghent University Hospital, Radiation Oncology, Ghent, Belgium; 3 Universitätsklinikum Augsburg, Radiation Oncology, Augsburg, Germany; 4 University Medical Center Utrecht, Radiation Oncology, Utrecht, The Netherlands; 5 Amsterdam Univerisity Medical Center, Radiation Oncology, Amsterdam, The Netherlands; 6 University Medical Center Schleswig- Holstein, Radiation Oncology, Kiel, Germany; 7 Technische Universität Dresden, Radiation Oncology, Dresden, Germany; 8 Kantonsspital Aarau , Radiation Oncology Center KSA-KSB, Aarau, Switzerland; 9 Charité-University Hospital Berlin, Radiation Oncology, Berlin, Germany; 10 Vall d'Hebron University Hospital, Radiation Oncology, Barcelona, Spain; 11 Technical University Munich, Radiation Oncology, Munich, Germany; 12 Schwarzwald-Baar Klinikum, Radiation Oncology, Villingen-Schwenningen, Germany; 13 Klinikum Stuttgart, Radiation Oncology, Stuttgart, Germany; 14 University of Freiburg, Radiation Oncology, Freiburg, Germany; 15 Instituut Verbeeten, Radiation Oncology, Tilburg, The Netherlands; 16 Ordensklinikum Linz, Radiation Oncology, Linz, Austria; 17 Catharina Hospital, Radiation Oncology, Eindhoven, The Netherlands; 18 Peter MacCallum Cancer Centre, Radiation Oncology, Melbourne, Australia; 19 University Hospital Frankfurt, Frankfurt, Frankfurt, Germany; 20 University Hospital Jena, Radiation Oncology, Jena, Germany; 21 University Hospital Würzburg, Radiation Oncology, Würzburg, Germany; 22 University Hospital Tübingen, Radiation Oncology, Tübingen, Germany; 23 Philipps-University Marburg, Radiation Oncology, Marburg, Germany; 24 Univerisity Hospital Zürich, Radiation Oncology, Zürich, Switzerland Purpose or Objective Stereotactic radiotherapy (SRT) is increasingly performed in patients receiving targeted therapy (TT) and/or immunotherapy (IT) to obtain a durable local control and possibly improve prognosis or prolong the time to systemic therapy switch. However, knowledge on the safety of this approach remains limited. The aim of this study was to prospectively collect real-life data and examine the safety of SRT combined with targeted therapy or immunotherapy in metastatic cancer patients. Materials and Methods Metastatic cancer patients receiving SRT concurrent (≤30d) to any type of TT or IT were included in this international multicenter prospective register database (TOaSTT). Patients received SRT of brain metastases (BM) or extracranial lesions. Treatment-related toxicity was measured using the CTCAE v4.03 criteria. The primary endpoint of this study was severe acute (≤3 months) and late (>3 months) toxicity within one year following SRT. Results Between July 2017 and August 2019, 1031 SRTs were performed in 479 patients from 27 centers. Patients were followed up for a minimum of 12 months. Most frequent histologies were NSCLC (37%), melanoma (36%), RCC (8%) and breast cancer (6%). Median age was 62 (range 26-88) years, ECOG-PS was 0-1 in 92% of patients. SRT of brain or extracranial metastases was performed in 273 and 208 patients, respectively. Median GTV volume was 2.1cc (range 0.1-54) for BM and 9.9cc (range 0.1-267) for extracranial lesions. The median prescribed dose was 20 Gy in 1 fraction for BM and 30Gy in 5 fractions for extracranial lesions. A median of 1 (range 1-15) lesions were treated simultaneously. SRT was combined with immune checkpoint inhibitors (ICI) (51%), ICI combined with targeted agents (TT) (10.4%), TT (29.4%) or antibodies (9%). TT/IT was started before SRT in 69%, with a median of 112 days (range 1-2751), 31% of patients started TT/IT concurrent with SRT, a median of 10 (range 1-30) days after SRT. TT was interrupted during SRT in 15% of patients, with a median break of 6 (range 1-56) days. Any grade acute and late SRT-related toxicity occurred in 50% and 44% of patients, respectively. Severe acute toxicity occurred in 6.6% of BM-SRT patients, including n=3 G5 toxicities. After extracranial SRT, severe acute toxicity was observed in 4.3% patients, with no G5 observed. Severe late toxicity was observed in 8.2% BM-SRT patients and 3.4% extracranial SRT patients. There was no significant